Interpretive Summary: Strawberries are a major dietary source of ellagic acid-containing compounds which demonstrate anticancer activity, anti-inflammatory effect, and prevention of heart disease by decreased oxidation of low-density lipoprotein and platelet aggregation. Strawberry purees are produced commercially; some are consumed directly, while others are used as intermediate products and ingredients for juices, smoothies, fruit fillings, yoghurt, and jams or jellies, etc. In a bar or restaurant setting, strawberry purees are directly added to smoothies, used as ice cream toppings, etc. without any further thermal treatment. Therefore, it is important to ensure that the purees contain no pathogens. Foodborne pathogens including Escherichia coli O157:H7 have been reported to be capable of survival in raw fruit and vegetable juices. In this study, films of polylactic acid (PLA) polymer incorporated with nisin, ethylenediaminetetraacetic acid (EDTA), potassium sorbate (PS), sodium benzoate (SB), and their combination were developed and their effects on the inactivation of E. coli O157:H7, total aerobic bacteria, molds and yeasts in strawberry puree were determined. This study demonstrated that preservatives retained more antimicrobial activity when they were incorporated into PLA films while nisin, EDTA, SB and PB in combination achieved significant reductions of native microflora and inoculated populations of E. coli O157:H7. Data from this study suggested that antimicrobial packaging is an effective approach to ensure food safety and extend food shelf life.

Technical Abstract:
Antimicrobial films of polylactic acid polymer incorporated with nisin, Ethylenediaminetetraacetic acid (EDTA), sodium benzoate (SB), potassium sorbate (PS) and their combination were developed and their antimicrobial effects on the inactivation of Escherichia coli O157:H7 and natural background microflora (total aerobic bacteria, molds, and yeasts) in strawberry puree was determined at 10 and 22 C. Direct addition of SB+PS to strawberry puree was also used as a comparison. The combination treatment reduced the cell populations of E. coli O157:H7 from 3.5 log CFU/ml to undetectable levels (<1 CFU/ml) after 14 days and 1 day at 10 and 22C, respectively, while the cells of E. coli O157:H7 in control samples survived up to 48 days at 10C and more than 14 days at 22C. The SB+PS film treatment reduced more cells of E. coli O157:H7 than that of the SB+PS direct addition treatment. Similar results were observed for inactivation of natural microflora. In general, the antimicrobial effect was in the following order: film combination > SB+PS film > SB+PS direct addition > EDTA film > nisin film. The data in this study suggested two approaches to improving antimicrobial effectiveness on inactivating E. coli O157:H7 and extending microbiological shelf life of strawberry puree: (1) using antimicrobial packaging and (2) using combinations of preservatives. The developed film formula can be used to make bottles or as coatings on the surface of bottles for use in liquid food packaging.